The present invention relates to a method of machining a rare earth alloy, and more particularly, it relates to a method of grinding and cutting a rare earth alloy suitably used as a material for a magnet.
A rare earth alloy is used, for example, as a material for a powerful magnet. A rare earth magnet obtained by magnetizing a rare earth alloy is suitably used, for example, as a material for a voice coil motor for use in positioning a magnetic head of a magnetic recording device.
As a method of cutting a rare earth magnet, Japanese Laid-open Patent Publication No. 9-174441 discloses use of a peripheral cutting edge (sometimes designated as xe2x80x9ca grinding wheelxe2x80x9d or xe2x80x9ca grindstonexe2x80x9d) with a cutting part onto which diamond abrasive particles are adhered in a ratio of 10 through 80%.
Also, the applicant of the base Japanese application of the present application has proposed, in Japanese Laid-Open Patent Publication No. 61-264106, a method of machining a Rxe2x80x94Fexe2x80x94B rare earth alloy with a diamond grinding wheel or the like in a non-oxidizing oil for preventing oxidation of the surface of the rare earth alloy.
As a result of various examination of the method of machining a rare earth alloy, however, the present inventors have found that the conventional methods have problems described below. In particular, in order to efficiently and precisely machine a rare earth alloy having a main phase where brittle fracture is caused and a boundary layer where ductile breaking is caused, such as a rare earth alloy prepared by sintering (hereinafter referred to as the xe2x80x9crare earth sintered alloyxe2x80x9d), it is necessary to efficiently release heat generated in machining, namely, to cool a part to be machined.
For example, even when the grinding wheel disclosed in Japanese Laid-Open Patent Publication No. 9-174441 is used, the temperature of the grinding edge abnormally increases unless a part to be machined is efficiently cooled, and the abnormally high temperature can cause abnormal abrasion of the grinding edge or abnormally large loss of the diamond abrasive particles. The abnormal abrasion and the abnormally large loss can disadvantageously degrade the machining preciseness as well as increase the machining cost because the life of the expensive grinding wheel is shortened. This publication does not mention anything about cooling a part to be machined.
Furthermore, in the method disclosed in Japanese Laid-Open Patent Publication No. 61-264106, although the non-oxidizing oil can suppress the oxidation, it is difficult to sufficiently cool the grinding wheel including the diamond abrasive particles.
The present invention was devised to overcome the aforementioned problems, and an object is providing a method of highly precisely and efficiently machining a rare earth alloy and a method of fabricating a rare earth magnet using the same.
The method of machining a rare earth alloy of this invention includes the steps of providing a block of the rare earth alloy; rotatably supporting a grinding wheel having, on a peripheral portion thereof, a grinding edge including diamond abrasive particles; and grinding the block of the rare earth alloy by bringing the grinding edge into contact with the block, with the grinding wheel rotated and with a coolant having surface tension of 25 mN/m through 60 mN/m supplied to the grinding edge of the grinding wheel. As a result, the above-described object is achieved.
Alternatively, the method of machining a rare earth alloy of this invention includes the steps of providing a block of the rare earth alloy; rotatably supporting a grinding wheel having, on a peripheral portion thereof, a grinding edge including diamond abrasive particles; and grinding the block of the rare earth alloy by bringing the grinding edge into contact with the block, with the grinding wheel rotated and with a coolant having a coefficient of dynamic friction against the rare earth alloy of 0.1 through 0.3 supplied to the grinding edge of the grinding wheel. As a result, the above-described object is achieved.
The coolant preferably includes water as a main component. Also, the coolant preferably includes an antifoaming agent. In addition, the coolant preferably has pH of 9 through 11. The coolant preferably further includes a rust inhibitor.
In the method of machining a rare earth alloy, the grinding edge of the grinding wheel preferably further includes a phenol resin and includes the diamond abrasive particles in a. volume ratio of 10 through 80%. Preferably, the grinding wheel has a disk-shaped base plate, the grinding edge is disposed on a peripheral portion of the base plate, and the base plate is made from a sintered hard alloy.
In the method of machining a rare earth alloy, the rare earth alloy can be a Rxe2x80x94Fexe2x80x94B rare earth sintered alloy.
The coolant is preferably jetted toward the grinding edge.
The method of machining a rare earth alloy may further include the steps of collecting sludge including grinding waste of the rare earth alloy and the coolant produced in the step of grinding the block; and separating the grinding waste of the rare earth alloy from the collected sludge by using a magnet.
When the step of grinding the block includes a step of moving the grinding wheel relatively to the block, the block can be cut into pieces by the present method of machining a rare earth alloy.
Preferably, in the step of grinding the block, a rotating speed of the grinding wheel, a cutting speed and a pressure for jetting the coolant are adjusted, whereby a force Fx along a tangent of the grinding wheel and a force Fz along a radial direction of the grinding wheel applied to the block respectively fall within predetermined ranges.
The method of machining a rare earth alloy preferably further includes the steps of monitoring the force Fx and the force Fz; and determining whether or not the force Fx and the force Fz respectively are within the predetermined ranges.
The method of fabricating a rare earth magnet of this invention includes the steps of providing a block of the rare earth alloy; rotatably supporting a grinding wheel having, on a peripheral portion thereof, a grinding edge including diamond abrasive particles; grinding the block of the rare earth alloy by bringing the grinding edge into contact with the block, with the grinding wheel rotated, with a coolant having surface tension of 25 mN/m through 60 mN/m supplied to the grinding edge of the grinding wheel, and with the grinding wheel moved relatively to the block, whereby the block is cut into pieces; and magnetizing the rare earth alloy. As a result, the above-described object is achieved. The method of fabricating a rare earth magnet of this invention is practiced by using the aforementioned method of machining a rare earth alloy.